1. Field of the Invention
The invention relates to a vehicle behavior control system and method that executes the turning radius reduction control and the traction control.
2. Description of the Related Art
The minimum turning radius of a vehicle is determined based on the characteristics of the vehicle such as the wheel base and the maximum steering angle. When a vehicle makes a U-turn or is turned into a narrow parking space, the vehicle is sometimes required to turn at a turning radius smaller than its minimum turning radius. In this case, the driver needs to perform extra vehicle operations, for example, turn the vehicle in a K-turn. Especially, when driving a vehicle having a long wheel base, for example, a mini-van, the driver needs to perform some annoying vehicle operations because the minimum turning radius of such a vehicle is large. Therefore, a system that reduces the turning radius of a vehicle to below its minimum turning radius, which is determined based on the characteristics of the vehicle, (hereinafter, such a system will be referred to as a “turning radius reduction system”) has been developed. Such a system enables the vehicle to turn in a smaller radius. Japanese Patent Application Publication No. JP-2006-103517 descries a system that controls braking forces when a vehicle is turning, such that the braking force applied to inner wheels is larger than the braking force applied to outer wheels (especially, a great braking force is applied to the rear inner wheel), and controls drive power such that the vehicle speed is equal to or higher than a predetermined value.
Some rear drive vehicles include a traction control system in addition to the above-described turning radius reduction system. In the traction control, a braking force is applied to a drive wheel (rear wheel) in accordance with the degree of slip of the drive wheel with respect to that of a reference wheel, whereby spinning of the drive wheel is suppressed. The wheel turning at a low wheel speed is usually used as the reference wheel. If the turning radius reduction control is executed while the vehicle is turning, the wheel speed of the rear inner wheel becomes considerably lower than the wheel speeds of the other wheels, because the braking force is applied to the rear inner wheel by the turning radius reduction control and the turning radius of the inner wheel is smaller than that of the outer wheel. Accordingly, when the turning radius reduction control is executed, the rear inner wheel is used as the reference wheel and therefore the degree of the slip of the rear outer wheel is considerably high with respect to that of the reference wheel. Accordingly, even when the traction control need not be executed (even when the drive wheel is not actually spinning), the traction control may be executed and a braking force may be applied to the rear outer wheel. Therefore, a braking force is applied to the rear inner wheel by the turning radius reduction control and a braking force is applied to the rear outer wheel by the traction control. As a result, braking forces are applied to both the right and left drive wheels, which leads to deterioration in the driving performance of the vehicle.